There are numerous prior art photocoagulation systems described in the prior art. Examples of these may be found in the U.S. patents corresponding to the following U.S. Pat. Nos. 2,930,379 (Dopp, et al.); 3,096,767 (Gresser, et al.); 3,467,099 (Lotmar); 3,348,547 (Kavanagh); 3,456,651 (Smart); 3,487,835 (Koester, et al.); 3,720,213 (Hobart, et al.); 3,783,874 (Koester, et al.); 3,809,092 (Abraham); 3,930,504 (de Laforcade); and 3,982,541 (L'Esperance). In all of these patents, a laser beam is disclosed as being directed through the pupil of a patient's eye to be concentrated upon selected areas of the fundus. The laser beam is directed by means of a mirror which rotates or oscillates so as to direct the reflected laser beam accordingly. The laser beam may be directly incident upon the cornea or upon a contact lens placed over the cornea. When oscillated by the oscillating mirror, the laser beam hits the cornea or contact lens at different incidence angles. Under such circumstances, a certain amount of astigmatism is introduced into the laser beam in an amount determined by the angle of incidence. This astigmatism changes to distribution and the density of the energy in the laser beam, resulting in irregularities in the photocoagulation procedure.
In those photocoagulation systems employing a contact lens over the cornea, another problem results. Specifically, it is difficult, when using the contact lens, to achieve the proper depth of focus on the fundus of the eye.
The prior art systems which employ direct ophthalmoscope observation techniques (such as Smart, Kavanagh, Dopp, et al., Gresser, et al., de Laforcade) provide sufficient magnification of the image of the patient's fundus as viewed by the operator. However, the field is very small and there is no stereoscopic viewing. In the Koester, et al. patents, monocular indirect ophthalmoscopic viewing is employed and provides a somewhat larger field, but no stereoscopic viewing and very low magnification.